The cross sections for boron isotope production in carbon spallation by 40, 50, 150, 600 MeV, 25 GeV protons and 100-160 MeV $\alpha$ particles have been measured. Isotope ratio measurements were performed by sputtering mass spectrometry. An isotope dilution-like method in solid phase was developed for absolute cross section measurements. The present work and previous experimental results allow cosmic ray propagation calculations based mainly on experimental cross section values. The abundances of the light cosmic ray elements were calculated using the "leaky-box" model. The variations of the abundances of light secondary elements are accounted for by a rigidity dependence of the mean free path against escape. The density of the propagation medium is discussed using the ${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ decay. The calculated values of the boron and lithium isotopic ratios in cosmic rays, practically independent of the propagation assumptions, are found to be independent of the energy from 1 to 100 GeV per nucleon.

NUCLEAR REACTIONS $\mathrm{C}(p,x)$, $\mathrm{C}(\alpha ,y)$, $E=40,50,150,600$ MeV, 25 GeV protons, 100-160 MeV $\alpha$ particles; measured $\sigma \text{'}\mathrm{s}$; natural target; mass spectrometry. Propagation of light cosmic ray nuclei.

• Received 27 May 1976

DOI:https://doi.org/10.1103/PhysRevC.15.2159